1. Field of the Invention
The present invention relates to a piezoelectric actuator for a liquid transporting apparatus, a method for producing piezoelectric actuator, a liquid transporting apparatus and a method for producing liquid transporting apparatus.
2. Description of the Related Art
A liquid transporting apparatus such as an ink-jet head or the like for discharging ink from a nozzle is provided with an actuator for applying a pressure to a fluid so as to transport the fluid. Various configurations can be adopted for such actuators, but of these configurations, piezoelectric actuators in which a piezoelectric layer formed of a ferroelectric piezoelectric material such as lead zirconium titanate (PZT) is provided and deformation of the piezoelectric layer when an electric field is acting thereon are utilized to drive a subject are widely employed. For example, unimorph-type piezoelectric actuators used in ink-jet heads are typically provided with a vibration plate covering a pressure chamber accommodating ink, a piezoelectric layer arranged on a side of the vibration plate opposite to the pressure chamber, and two electrodes which are arranged on both sides of the piezoelectric layer respectively.
When a drive voltage is applied to one of the electrodes of this piezoelectric actuator, an electric field acts on the piezoelectric layer sandwiched between the two electrodes in a thickness direction and this portion of the piezoelectric layer extends in the thickness direction and contracts in a direction parallel to a plane of the piezoelectric layer. At this time, accompanying deformation of the piezoelectric layer, the vibration plate also deforms, due to which the volume of the pressure chamber changes, thereby applying pressure to ink in the pressure chamber.
The method for forming a piezoelectric layer includes, for example, an aerosol deposition method (AD method, for example, see Patent Document 1) in which extremely small particles of piezoelectric material are mixed with a carrier gas and blown against a substrate so as to collide the particles with the substrate at high speed so as to deposit the particles on the substrate, or a sputtering method (for example, see Patent Document 2) in which particles of a target are deposited on a substrate by ionizing argon or the like and causing the ionized argon to collide with the target.
[Patent Document 1] Japanese patent application laid-open No. 2003-142750.
[Patent Document 2] U.S. Pat. No. 6,347,862 and corresponding Japanese patent application laid-open No. 10-286953.
However, when particles of piezoelectric material are deposited on a vibration plate so as to form a piezoelectric layer using the AD method and sputtering method described above, there are cases in which the thickness of the piezoelectric layer deviates and fluctuates from a target value (design value). When thickness of a piezoelectric layer fluctuates within one piezoelectric actuator, the amount of deformation of the vibration plate is different for each of pressure chambers. There are therefore fluctuations in ink jetting characteristics such as droplet volume and droplet speed of the ink or the like which cause printing quality to deteriorate. Further, when fluctuation occurs in piezoelectric layers between a plurality of ink-jet heads, the thickness of the piezoelectric layer deviates from a predetermined range so that it is not possible to implement printing of the desired quality. In this case, yield rate falls.